The present invention relates in general to pulverizers and in particular to a new and useful pulverizer roller assembly with a pop off relief valve.
MPS type pulverizers are known from STEAM/ITS GENERATION AND USE, 39TH Edition, the Babcock & Wilcox Company, 1978, pp 9-7, 9-8. This, and any similar type of pulverizer utilizes a bearing support for a plurality of rollers that rolls in a race for crushing and pulverizing various materials, in particular coal.
Each roller or roll wheel assembly in an MPS or other similar pulverizer, is supported by a bearing structure with an enclosed oil supply. The oil supply is required to both cool and lubricate the internal bearing parts. During operation, air and gases within the enclosed oil supply space, heat up and expand. If this expansion is not released, damage will result to components in the bearing structure such as lip seals and O-rings.
To relieve this pressure buildup, a pop off relief valve is located in a remote area of the roll wheel assembly. This relief valve vents the expanded gas into a chamber containing seal air. Although a porous fixture has been considered for relieving this pressure buildup, a relief valve is used instead so that pressure tests can be conducted on the oil chamber using pressurized air.
Referring to FIG. 1, the known roll wheel assembly for an MPS pulverizer comprises a roller bracket 10 having an opening 11 which carries the outer end of a roll wheel shaft 12. A roll wheel 14 is mounted for rotation on an inner end of shaft 12 by a pair of axially spaced bearings 16 and 18. A space for lubricating and cooling oil is defined between the bearings and between an outer bearing spacer 20 and an inner bearing spacer 22 which circumferentially surround the shaft 12. A tire 24 of wear resistant material, is fixed to wheel 14, by an interference fit and a clamp ring 26 which is bolted to wheel 14. A ring shaped roller seal retainer 28 is connected by cap screws 30 to wheel 14 for rotation with the wheel. A lip seal assembly 32 retained by retainer 28, is slidably engaged against a ring shaped roll seal sleeve 34. Shaft 12 is retained in position on roller bracket 10 by a shaft retainer 36 bolted over an outer end face of the shaft 12 and shaft 12 is rotationally fixed to roller bracket 10 by a key 38. The bearings and spacers are held in position by a bearing retainer 40. Retainers 36 and 40 are bolted to opposite ends of shaft 12.
To keep the oil in the space around shaft 12, O-ring 45 is clamped between the wheel 14 and retainer 28 and two O-rings 47 are clamped within recesses in the shaft 12 and roll seal sleeve 34. The lip seal assembly 32 creates a rotating oil seal with the roll seal sleeve 34. The end of shaft 12 is further sealed by a plug 52 and O-ring 49. A bearing cover 42 is bolted to wheel 14 over an axial end of the space. An O-ring 44 is located between the bearing cover 42 and the wheel 14.
To insure that sufficient force is applied to the tire 24 downwardly onto the rack (not shown), pressure is applied to the bracket 10 by a pressure frame (not shown), at a roll pin block 46 which carries a roll pivot 48.
Oil is supplied to the oil space or chamber by an oil conduit 50 having an outer end closed by the plug 52 and O-ring 49. The opposite end of oil conduit 50 opens at the far end of the oil chamber. A radial extension 54 from oil conduit 50 is an internal vent which allows oil and gas to flow into the space around shaft 12 and under inner spacer 22.
A lubricating channel 56 is also provided in shaft 12 for communicating with the inner surface of sleeve 34.
As illustrated in FIG. 2, which is a greatly enlarged sectional view of an area around the roll seal retainer 28, roll seal sleeve 34 includes an axial passage 58 having an inner opening communicating with the oil chamber, and an outer opening covered by a pop off relief valve 60. When excess gas pressure occurs within the oil chamber, valve 60 opens and discharges the gas into an air seal space 62. A roll air seal 64 which is fixed to bracket 10 by cap screws 66, closes the air seal space and is slidably engaged with the roller seal retainer 28. Two lip seals 32 separate the oil space from the air seal space 62.
A major problem in maintaining the pop off relief valve 60 is its remote location. Since the pop off relief valve is a mechanical device which is sensitive to contamination, it requires periodic inspection and service. To inspect the valve, the roll wheel assembly must be removed from the pulverizer. For an MPS type pulverizer, three such assemblies are used in each pulverizer. This of course requires the pulverizer to be taken out of operation. The internal structure of the pulverizer must also be supported when removing the roll wheel assembly. The roll wheel assembly is also not easily removed since it may weigh as much as 35,000 pounds.
Once removed, each assembly must be further disassembled for access to the pop off relief valve in each assembly.